The present invention relates to an improved automotive headlamp using a metal halide lamp bulb as a light source.
Automotive headlamps using a metal halide discharge lamp bulb 50 as a light source are known, examples of which are shown in see FIGS. 8(a) and 8(b). In the metal halide discharge lamp bulb 50 part of the metal halide tends to sediment on the bottom of the discharge lamp bulb (arrow A). The metal halide sediment 51 scatters light, and the scattered light is reflected by the bottom of a reflector 52 (arrow B), producing upward flaring light G1, as shown in light distribution patterns of FIG. 9. This flaring light, that is, the portion of the light distribution attributed to the scattered light, at a portion to the right of a vertical line V and over a horizontal line H can temporarily blind the driver of an oncoming vehicle. On the other hand, the driver of the automobile producing such flaring light cannot see obstacles in the road unless a sufficient amount of light is provided in certain portions of the light distribution. Further, as is apparent from FIG. 9, the automotive headlamp of this type has problems in that the amount of light is so large as to produce flaring light at a portion G2 close to highly intense portions S1 and S2 even in the absence of the flaring light G1 resulting from the halide sediment 51, and in that the amount of light is so small at peripheral portions, such as a portion G3, that visibility for obstacles in the road is low.
Therefore, what has long been desired is an automotive headlamp of a type employing a metal halide discharge lamp bulb which produces no flaring light G1 associated with light scattered by halide sediments and less light distribution at the upper right portion G2 surrounded by the lines V and H, and which provides a certain desired amount of light at the peripheral portion G3.